The advent of Personal Communication Services (PCS) has resulted in a tremendous increase in the demand for spectrum. To meet this demand, different service providers might have to share the scarce spectrum allocated, necessitating several different access schemes employing different modulation techniques to co-exist. Since optimum spectral re-use is of primary concern, estimation of both co-channel and adjacent channel (i.e., "interchannel") interference from interferers in the same system (due to frequency re-use) as well as from other systems and services sharing the same band is very important. While the effects of adjacent channel interference can be mitigated by good filter design and good frequency planning techniques, co-channel interference remains as a limiting factor for systems sharing the same band. Additionally, the interference between co-existing networks is a source of regulatory problems.
One particular type of interference which is becoming more prevalent is interference on systems which use analog (e.g., phase modulated (PM)) signals by systems which use digital (e.g., QPSK or MSK) signals. This type of interference is becoming more prevalent because, while the majority of present systems are analog, users are switching to digital systems because they are less prone to noise, they provide greater security against eavesdropping and theft of services, they permit cell phones to be smaller, lighter, and require less battery power than analog cell phones, and they provide services such as e-mail and headline news which are not available with analog systems. It can be appreciated, therefore, that techniques for optimizing spectrum efficiency with respect to digital signals are becoming increasingly important due to the expected scarcity in the bandwidth available for wireless communication systems. Spectrum-sharing enhances both the spectral utilization and the flexibility of that utilization and, as a result, provides additional capacity to networks. However, to obtain optimal spectral re-use, channel allocation and channel spacing of co-existing systems must be coordinated.
The effects of interchannel interference on analog signals by digital signals are, however, different from the effects on analog signals by analog signals and are not well known in the prior art. Because the precise interference effects of digital signals on analog signals is not well known, the spectral re-use with respect to digital signals can not be optimized using conventional techniques.
Therefore, what is needed is a method for analyzing the interchannel interference effects of digital signals on analog signals and, furthermore, for utilizing such analysis to coordinate channel allocation and channel spacing of co-existing systems so that spectral re-use may be optimized when digital signals interfere with analog signals, and so that network capacity may be enhanced.